This invention relates to a resin composition, in particular, a resin composition having excellent heat resistance and mechanical properties and which comprises a maleimide-olefin copolymer in combination with a vinyl chloride resin.
Vinyl chloride resins have excellent chemical resistance and weather resistance properties and are relatively inexpensive. Therefore, they are widely used as general-purpose resin, for example in the production of building materials, such as rainwater gutters, pipes, tubes, corrugated sheets etc., for food-packaging purpose, in the production of parts of medical appliances, sundries and the like. However, in general, since vinyl chloride resins including vinyl chloride homopolymer and copolymers exhibit low heat resistance, their uses or applications are greatly restricted.
Thus, several ways of improving the heat resistance properties of vinyl chloride resins have been proposed, for example, blending a vinyl chloride resin with a chlorinated polyvinyl chloride resin, copolymerizing vinyl chloride monomer with another vinyl monomer, such as an N-substituted maleimide, blending a vinyl chloride resin with a copolymer of a styrene and/or methacrylate ester monomer with an N-substituted maleimide, and the like.
However, blending of a vinyl chloride resin with a chlorinated polyvinyl chloride resin will present a problem that the resulting resin composition is not satisfactorily improved in terms of heat resistance properties and is poor in processability and transparency properties. Further, in the case of copolymerizing vinyl chloride monomer with other vinyl monomer such as an N-substituted maleimide, there is a substantial difference in the copolymerization reactivity between vinyl chloride monomer and N-substituted maleimide monomer, that is the copolymerization reactivity of N-substituted maleimide is much higher than that of vinyl chloride monomer. Therefore, during copolymerization, there are produced N-substituted maleimide homopolymer and vinyl chloride homopolymer in addition to the desired vinyl chloride-N-substituted maleimide copolymer. Such a contaminated copolymer product tends to give moldings and formings of poor surface texture due to the difference in the melt-flow behavior between the polymeric components. Such poor surface texture leads to a problem of low mechanical properties of the moldings and formings. Further, blending a vinyl chloride resin with a copolymer of styrene and/or a methacrylate ester with an N-substituted maleimide gives rise to a problem that the resulting blend composition will exhibit low transparency and poor mechanical properties due to low compatibility between the vinyl chloride resin and said N-substituted maleimide copolymer and also a large difference in the processing temperature between the vinyl chloride resin and the N-substituted maleimide copolymer.